Post-chemical mechanical polishing (CMP) cleaning method

ABSTRACT

Disclosed herein is a post-CMP cleaning method for effectively removing residues, including nitride particles and oxide particles produced in the chemical mechanical polishing (CMP) of a trench-buried oxide film and a pad oxide film as an etch barrier, which is carried out during a process of forming an isolation region in a semiconductor substrate using shallow trench isolation (STI). The post-CMP cleaning method comprises cleaning the substrate with a cleaning solution having a pH below 3 or above 9, so that the substrate surface, including the oxide film and the nitride film, has the same electric polarity as that of the nitride and oxide particles such that a repulsive force acts between the substrate surface and the nitride particles and between the substrate surface and the oxide particles, thereby effectively removing the nitride particles and the oxide particles.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for forming anisolation region in a silicon substrate using Shallow Trench Isolation(STI), and more particularly, to a post-chemical mechanical polishing(CMP) cleaning method for effectively removing nitride particlesproduced in a STI-CMP process.

[0003] 2. Description of the Prior Art

[0004] With the advancement of semiconductor technology, the high speedand high integration level of semiconductor devices are rapidlyincreased, and at the same time, requirements for a fine and precisepattern are gradually increased. These requirements are applied to apattern formed at an active region in a semiconductor substrate and alsoto an isolation region, which occupies a relatively large area.

[0005] In the prior art, the isolation region has been formed by a LOCOS(local oxidation of silicon) process. However, the isolation regionformed by the LOCOS process is disadvantageous in that a bird's beak isformed at its edge portion such that the area of the active region isreduced.

[0006] Thus, a method of forming an isolation region using a shallowtrench isolation (STI) process as substitute for the LOCOS process wasproposed, and the STI process is currently applied to form the isolationregion in most of semiconductor devices.

[0007] Hereinafter, the method for forming the isolation region in thesilicon substrate using the STI process will now be described.

[0008] First, a pad oxide film and a pad nitride film are successivelyformed on a semiconductor substrate, and patterned to expose portions ofthe substrate, which correspond to an isolation region. Then, theexposed region of the substrate is etched to form a trench.

[0009] Thereafter, the substrate is subjected to a sacrificial oxidationprocess to remove damages caused by the substrate etching, and then, awall oxide film is formed on the surface of the trench.

[0010] Next, a trench-buried oxide film, for example, an oxide filmformed by high density plasma chemical vapor deposition (hereinafter,referred to as HDP-oxide film), is deposited on the surface of thesubstrate in such a manner as to be buried in the trench. Then, thesurface of the HDP-oxide film is subjected to chemical mechanicalpolishing (hereinafter, referred to as CMP) until the pad nitride filmis exposed.

[0011] Then, the resulting substrate is cleaned, after which the padnitride film which was used as an etch barrier during the trench etch isremoved, thereby completing the formation of an isolation region.

[0012] However, the prior method for forming the isolation region usingthe STI process as described above has the following problems.

[0013] Generally, CMP of the interlayer insulating film made of an oxidefilm serves to polish only the oxide film, and thus, upon the subsequentcleaning, has no great connection with the pH of a cleaning solution. Inother words, even when a cleaning solution of any pH is used, oxideparticles having the same electric polarity as the interlayer insulatingfilm is produced and cannot be stuck again to the interlayer insulatingfilm.

[0014] However, materials polished in the STI-CMP process are twomaterials of the oxide film buried in the trench and the nitride filmused as the etch barrier, i.e., the oxide film and the nitride film.When these two materials are cleaned with a cleaning solution having apH of 3-9, they have opposite electric charges, so that there is a greatprobability that the oxide particles or the nitride particles, producedin CMP, are stuck to the oxide film or the nitride film, respectively.For this reason, badness in the CMP process and also deterioration indevice characteristics can occur. Particularly, when the polishedsubstrate is cleaned only with highly pure de-ionized (DI) water havinga pH below 7, the sticking of the nitride particles to the oxide filmcan become a serious problem.

SUMMARY OF THE INVENTION

[0015] Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and an object ofthe present invention is to provide a post-CMP cleaning method, whichallows the effective removal of the nitride and oxide particles producedin the CMP process.

[0016] To achieve the above object, the present invention provides apost-CMP cleaning method for removing residues including nitrideparticles and oxide particles produced in the chemical mechanicalpolishing (CMP) of a trench-buried oxide film and a pad oxide film as anetch barrier, which is carried out during a process of forming anisolation region in a silicon substrate using shallow trench isolation(STI), the post-CMP cleaning method comprising cleaning the siliconsubstrate with a cleaning solution having a pH below 3 or above 9, sothat the substrate surface, including the oxide film and the nitridefilm, has the same electric polarity as that of the nitride and oxideparticles such that a repulsive force acts between the substrate surfaceand the nitride particles and between the substrate surface and theoxide particles, thereby effectively removing the nitride particles andthe oxide particles.

[0017] Preferably, the cleaning solution used in the method according tothe present invention is maintained at a pH below 3 by the addition of astrong acid solution, such as a HF or HCl solution, or maintained at apH above 9 by the addition of a basic solution, such as a KOH or NaOHsolution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of thepresent invention will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

[0019]FIG. 1 is a graph showing the Zeta potential of an oxide film anda nitride film versus pH; and

[0020]FIGS. 2A and 2B are cross-sectional views for illustrating apost-CMP cleaning method according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 is a graph showing the Zeta potential of an oxide film anda nitride film versus pH. As shown in FIG. 1, the oxide film, such asSiO₂ and TiO₂, is electrically negative at a pH above 3, andelectrically positive at a pH below 3. The nitride film, such as Si₃N₄,is electrically positive at a pH below 9, and electrically negative at apH above 9. On the other hand, the oxide film and the nitride film havethe same electric polarity in the pH range between 3 and 9.

[0022] Thus, according to the present invention, the trench-buried oxidefilm and the pad nitride film, i.e., the oxide film and the nitridefilm, is maintained at a pH between 3 and 9. More concretely, accordingto the present invention, the substrate surface, including the oxidefilm and the nitride film, is maintained at the same electric polarityas that of the nitride particles, and at the same time, the substratesurface and the oxide particles are maintained at the same electricpolarity. This prevents the nitride particles and the oxide particlesfrom being stuck again to the substrate surface.

[0023] For this purpose, according to the present invention, after CMPof the trench-buried oxide film and the pad nitride film, a cleaningprocess for removing residues, including the nitride particles and theoxide particles produced by the CMP process, is carried out using acleaning solution maintained at a pH below 3 or above 9. In this case,the cleaning solution used in the method according to the presentinvention is maintained at a pH below 3 by the addition of a strong acidsolution, such as a HF or HCl solution, or maintained at a pH above 9 bythe addition of a basic solution, such as a KOH or NaOH solution.

[0024] As shown in FIGS. 2A and 2B, according to the present invention,a cleaning solution having a pH below 3 or above 9 is used in thepost-CMP cleaning of a substrate after subjecting a trench-buried oxidefilm 4 and a nitride film 3 to a CMP process. By the use of thiscleaning solution, the nitride and oxide particles 5 become electricallypositive, and at the same time, the substrate surface, including thetrench-buried oxide film 4 and the nitride film 3, becomes electricallypositive. Alternatively, the nitride and oxide particles 5 becomeelectrically negative, and at the same time, the substrate surfacebecomes electrically negative.

[0025] Thus, the substrate surface has the same electric polarity asthat of the oxide and nitride particles 5, so that the re-sticking ofthe particles 5 to the substrate surface can be prevented because of therepulsive force between the substrate surface and the particles 5.Accordingly, the nitride particles 5 can be effectively removed toimprove STI process reliability and also device characteristics.

[0026] In FIGS. 2A and 2B, the reference numerals 1 and 2 designate asilicon substrate and a pad oxide film, respectively.

[0027] As described above, according to the present invention, in orderto remove residues, including the nitride and oxide particles producedin the CMP process, the post-CMP cleaning of the substrate is carriedout using the cleaning solution having a pH below 3 or above 9. For thisreason, the substrate surface, including the oxide film and the nitridefilm, has the same electric polarity as that of the nitride and oxideparticles. Thus, a repulsive force acts between the substrate surfaceand the particles such that the particles can be effectively removed.

[0028] As a result, the reliability of the STI process including the CMPprocess can be ensured, and device characteristics can be improved.

[0029] Although a preferred embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A post-CMP cleaning method for removing residues,including nitride particles and oxide particles produced in the chemicalmechanical polishing (CMP) of a trench-buried oxide film and a pad oxidefilm as an etch barrier, which is carried out during a process offorming an isolation region in a semiconductor substrate using shallowtrench isolation (STI), the post-CMP cleaning method comprising cleaningthe substrate with a cleaning solution having a pH below 3 or above 9,so that the substrate surface, including the oxide film and the nitridefilm, has the same electric polarity as that of the nitride and oxideparticles such that a repulsive force acts between the substrate surfaceand the nitride particles and between the substrate surface and theoxide particles, thereby effectively removing the nitride particles andthe oxide particles.
 2. The method of claim 1, wherein the cleaningsolution is maintained at a pH below 3 by the addition of a HF or HClsolution.
 3. The method of claim 1, wherein the cleaning solution ismaintained at a pH above 9 by the addition of a KOH or NaOH solution.